I'm not sure if this is the right board, so please move it if it's in the wrong place, anyway... I had to replace my Shimano cartridge BB (Square taper UN something, I can't think of the number). The worn out one was all metal, both the bit which houses the bearings and the piece which screws in the other side. When I got the new one I found that the piece for the other side had been changed to plastic. I couldn't just swap the old one over as they didn't quite fit. I think it's bad enough that the unit is sealed (although it seems like it is possible to overhaul it, I might try to refit the old one with new bearings), but to put plastic in means that it's life is limited to the plastic becoming brittle and aged. I also nearly cross threaded it the first time I tried to fit it, and also had no idea how tight I could do it up before I stripped the threads.
I know that it's very likely I'll wear the bearings out long before the plastic gives up, but the whole idea of selling something so flimsy and throwaway really annoyed me. I'll definitely switch to a different brand if I can track down something which is all metal. Has anyone else had a problem with this or am I just moaning about nothing?